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This invention relates to improved methods and apparatus for completing wells, and more particularly, to improved methods and apparatus for gravel packing, fracturing or frac packing by providing multiple flow paths for slurry flow via bypass tubes or conduits in the well annulus.
The production of hydrocarbons from unconsolidated or poorly consolidated formations may result in the production of sand along with the hydrocarbons. The presence of formation fines and sand is disadvantageous and undesirable in that the particles abrade pumping and other producing equipment and reduce the fluid production capabilities of the producing zones in the wells.
Particulate material (e.g., sand) may be present due to the nature of a subterranean formation and/or as a result of well stimulation treatments wherein proppant is introduced into a subterranean formation. Unconsolidated subterranean zones may be stimulated by creating fractures in the zones and depositing particulate proppant material in the fractures to maintain them in open positions.
Gravel packs with sand screens and the like have commonly been installed in wellbores penetrating unconsolidated zones to control sand production from a well. The gravel packs serve as filters and help to assure that fines and sand do not migrate with produced fluids into the wellbore.
Cased-hole gravel packing requires that the perforations or fractures extending past any near-wellbore damage as well as the annular area between the outside diameter (OD) of the screen and the inside diameter (ID) of the casing be tightly packed with gravel. See Brochure: xe2x80x9cSand Control Applications,xe2x80x9d by Halliburton Energy Services Inc., which is incorporated herein by reference. The open-hole gravel-pack completion process requires only that the gravel be tightly packed in the annulus between the OD of the screen and the openhole.
Several techniques to improve external gravel-pack placement, either with or without fracture stimulation, have been devised. These improved techniques can be performed either with the gravel-pack screen and other downhole equipment in place or before the screen is placed across the perforations. The preferred packing methods are either 1) prepacking or 2) placing the external pack with screens in place, combined with some sort of stimulation (acid-prepack), or with fracturing or acidizing. The xe2x80x9cacid-prepackxe2x80x9d method is a combination stimulation and sand control procedure for external gravel-pack placement (packing the perforations with gravel). Alternating stages of acid and gravel slurry are pumped during the treatment. The perforations are cleaned and then xe2x80x9cprepackedxe2x80x9d with pack sand.
Combination methods combine technologies of both chemical consolidation and mechanical sand-control. Sand control by chemical consolidation involves the process of injecting chemicals into the naturally unconsolidated formation to provide grain-to-grain cementation. Sand control by resin-coated gravel involves placing a resin-coated gravel in the perforation tunnels. Resin-coated gravel is typically pumped as a gel/gravel slurry. Once the resin-coated gravel is in place, the resin sets up to form a consolidated gravel filter, thereby removing the need for a screen to hold the gravel in place. The proppant pumped in a frac treatment may be consolidated into a solid (but permeable) mass to prevent proppant-flow back without a mechanical screen and to prevent formation sand production. U.S. Pat. No. 5,775,425, which is incorporated herein by reference, discloses an improved method for controlling fine particulates produced during a stimulation treatment, including the steps of providing a fluid suspension including a mixture of a particulate coated with a tackifying compound and pumping the suspension into a formation and depositing the mixture within the formation.
A combined fracturing and gravel-packing operation involves pumping gravel or proppant into the perforations at rates and pressures that exceed the parting pressure of the formation. The fracture provides stimulation and enhances the effectiveness of the gravel-pack operation in eliminating sand production. The fracturing operation produces some xe2x80x9crestressingxe2x80x9d of the formation, which tends to reduce sanding tendencies. See Brochure: xe2x80x9cSTIMPAC Service Brochure,xe2x80x9d by Schlumberger Limited, which is incorporated herein by reference. The high pressures used during fracturing ensure leakoff into all perforations, including those not connected to the fracture, packing them thoroughly. Fracturing and gravel packing can be combined as a single operation while a screen is in the well.
xe2x80x9cFracpackingxe2x80x9d (also referred to as xe2x80x9cHPF,xe2x80x9d for high-permeability fracturing) uses the tip-screenout (TSO) design, which creates a wide, very high sand concentration propped fracture at the wellbore. See M. Economides, L. Watters and S. Dunn-Norman, Petroleum Well Construction, at 537-42 (1998), which is incorporated herein by reference. The TSO occurs when sufficient proppant has concentrated at the leading edge of the fracture to prevent further fracture extension. Once fracture growth has been arrested (assuming the pump rate is larger than the rate of leakoff to the formation), continued pumping will inflate the fracture (increase fracture width). The result is short but exceptionally wide fractures. The fracpack can be performed either with a screen and gravel-pack packer in place or in open casing using a squeeze packer. Synthetic proppants are frequently used for fracpacks since they are more resistant to crushing and have higher permeability under high confining stress.
In a typical gravel pack completion, a screen is placed in the wellbore and positioned within the zone which is to be completed. The screen is typically connected to a tool which includes a production packer and a crossover port, and the tool is in turn connected to a work string or production string. A particulate material, which is usually graded sand, often referred to in the art as gravel, is pumped in a slurry down the work or production string and through the crossover port whereby it flows into the annulus between the screen and the wellbore and into the perforations, if applicable. The liquid forming the slurry leaks off into the subterranean zone and/or through the screen which is sized to prevent the sand in the slurry from flowing therethrough. As a result, the sand is deposited in the annulus around the screen whereby it forms a gravel pack. The size of the sand in the gravel pack is selected such that it prevents formation fines and sand from flowing into the wellbore with produced fluids.
Circulation packing (sometimes called xe2x80x9cconventionalxe2x80x9d gravel-packing) begins at the bottom of the screen and packs upward along the length of the screen. Gravel is transported into the annulus between the screen and casing (or the screen and the open hole) where it is packed into position from the bottom of the completion interval upward. The transport fluid then returns to the annulus through the washpipe inside the screen that is connected to the workstring.
Horizontal gravel packs can be placed in open or cased hole completions of varying lengths. The alpha/beta wave approach has been used extensively for gravel packing horizontal wells. See Dickinson, W. et al.: xe2x80x9cA Second-Generation Horizontal Drilling System,xe2x80x9d paper 14804 presented at the 1986 IADC/SPE Drilling Conference held in Dallas, Tex., February 10-12; Dickinson, W. et al.: xe2x80x9cGravel Packing of Horizontal Wells,xe2x80x9d paper 16931 presented at the 1987 SPE Annual Technical Conference and Exhibition held in Dallas, Tex., September 27-29; and M. Economides, L. Watters and S. Dunn-Norman, Petroleum Well Construction, at 533-34 (1998), which are all incorporated herein by reference. This method is a two-step procedure, which includes an alpha wave sand deposition in one direction and a beta wave sand deposition in the opposite direction. Water-based sand slurry is pumped down the vertical work string out the horizontal portion of the screen-casing annulus. A sand dune builds up in the borehole both in the forward direction (away from the vertical borehole) and in the reverse direction (back toward the vertical borehole). The sand dune fills the horizontal borehold annulus to about 50% to over 80% fill (the alpha sand wave deposition). The leading edge of the sand dune progresses toward the toe of the wellbore until it reaches the end of the screen. Then the beta wave deposition of sand in the horizontal borehole begins. The sand movement in the beta deposition occurs in successive waves. However, this approach depends on maintaining a very limited fluid loss. If fluid loss is too great, it will stall the completion of alpha wave development, allowing a beta wave to start or causing a bridge to form that prevents the annular pack from being completed.
A problem often encountered in forming gravel packs, particularly gravel packs in long and/or deviated unconsolidated producing intervals, is the formation of sand bridges in the annulus between the sand retainer screen and the casing wall (for in-casing gravel packs) or the formation (for open-hole gravel packs). Non-uniform sand packing often occurs as a result of the loss of carrier liquid from the sand slurry into high permeability portions of the subterranean zone. This in turn causes the formation of sand bridges before all the sand has been placed. Sand bridges in the interval to be packed prevent placement of sufficient sand below that bridge for top-down gravel packing, or above that bridge for bottom-up gravel packing. When the well is placed on production, the flow of produced fluids is concentrated through the voids in the gravel pack, which soon causes the screen to be eroded, and the migration of fines and sand with the produced fluids to result.
The key to successful frac packs and gravel packs is complete packing of gravel in the fracture, perforations and well annulus. The development of bridges in long perforated intervals or highly deviated wells can end the treatment prematurely, resulting in reduced production from unpacked perforations, voids in the annular gravel pack, and/or reduced fracture width and conductivity.
To prevent the formation of sand bridges and create uniform distribution during gravel packing, xe2x80x9calternate-pathxe2x80x9d (or xe2x80x9cmultiple-pathxe2x80x9d) well screens using perforated xe2x80x9cshunt tubesxe2x80x9d extending along the screen have been proposed. See, e.g., Jones, L. G., et al.: xe2x80x9cAlternate Path Gravel Packing,xe2x80x9d SPE 22796, 1991 and L. Jones: xe2x80x9cSpectacular Wells Result From Alternate Path Technology,xe2x80x9d article reprint from Petroleum Engineer International, which are incorporated by reference herein for all purposes. In these well screens, the alternate-paths (e.g., perforated shunts or by-pass conduits) extend along the length of the screen and are in fluid communication with the gravel slurry as the slurry enters the well annulus around the screen. If a sand bridge forms in the annulus, the slurry is still free to flow through the conduits and out into the annulus through the perforations in the shunt tubes to complete the filling of the annulus above and/or below the sand bridge.
The shunts can be used in multiple intervals isolated by packers. See Brochure: xe2x80x9cAlternate Path Service Brochure,xe2x80x9d by Schlumberger Limited, which is incorporated herein for all purposes. The shunts are compatible with cup-type annular packers. Different sized tubes can be used for treating and packing different intervals. Shunts in different sizes can result in different flow rates.
In many alternate-path well screens, the individual shunt tubes are carried externally on the outer surface of the sand control screen. U.S. Pat. No. 4,945,991, which is incorporated herein by reference, proposes a well screen with perforated shunt tubes attached to the outside of a sand screen. This patent proposed attaching long, perforated shunt tubes to the exterior of the screen to form a continuous shunt path extending along the entire length of the screen, even when the screen was comprised of multiple sections. The shunt tubes were connected together between all sectional lengths of the screen, to provide a continuous flow path along the exterior of the screen sections for the gravel-laden fluid. (The patents and/or other references mentioned in the Background Section are not admitted to be xe2x80x9cprior artxe2x80x9d with respect to the present invention by their mere mention herein).
External shunt tubes suffer from numerous disadvantages and problems. See, e.g., U.S. Pat. No. 6,220,345 at col. 1, ln. 66-col. 2, ln. 24. Problems with the device of U.S. Pat. No. 4,945,991 are that it is troublesome to hang down the device in the wellbore and it is difficult to lift up the device from the wellbore due to the danger of the well screen sticking to the wellbore. Besides, it is extremely difficult to connect respective shunt tubes attached to the outside of the screen to shunt tubes attached to the outside of a following screen in the course of assembling the screen and lowering it into the wellbore.
Another disadvantage in mounting the shunts externally is that the shunts are exposed to damage during assembly and installation of the well screen. Due to the relative small size of the alternate-path shunt tubes, it is vitally important that they are not crimped or otherwise damaged during the installation of the screen. One proposal for protecting these shunts is to place them inside the outer surface of the sand retainer screen; see, e.g., U.S. Pat. Nos. 5,476,143 and 5,515,915, which are incorporated herein by reference. However, it may be more desirable from an economic standpoint to merely position and secure the by-pass conduits or shunt tubes onto the external surface of a commercially-available sand screen.
U.S. Pat. No. 5,934,376, which is incorporated herein by reference, discloses a new method, called CAPS(trademark), for concentric annular pack screen system, basically comprising the steps of placing a slotted liner or perforated shroud with an internal sand screen disposed therein, in the zone to be completed, isolating the perforated shroud and the wellbore in the zone and injecting particulate material into the annuli between the sand screen and the perforated shroud, and between the perforated shroud and the wellbore to thereby form packs of particulate material therein. The system enables the fluid and sand to bypass any bridges that may form by providing multiple flow paths via the perforated shroud/screen annulus and/or wellbore/screen annulus. See also Lafontaine, L. et al.: xe2x80x9cNew Concentric Annular Packing System Limits Bridging in Horizontal Gravel Packs,xe2x80x9d paper 56778 presented at the 1999 SPE Annual Technical Conference and Exhibition held in Houston, Tex., October 3-6, which is incorporated herein by reference.
U.S. Pat. No. 5,890,533, which is incorporated herein by reference, proposes a gravel-pack, well screen having a shunt tube positioned inside the base pipe of the screen. The shunt tube extends substantially throughout the length of the base pipe. A threaded connector or the like is provided on either end of the length of the internal shunt tube to connect the adjacent lengths of shunt tube together.
It is difficult and time consuming to make all the fluid connections between the respective shunt tubes which are required in making-up a typical alternate-path well screen. The use of thread joints to interconnect adjacent lengths or joints of well screen often makes it difficult to circumferentially align each pair of shunt tubes that must be interconnected to maintain axial continuity in the overall shunt flow path. Additionally, a supplemental connection fitting must be used to interconnect and operatively communicate the interiors of each pair of shunt tubes to be connected.
In making-up or assembling many alternate-path, well screens the desired number of joints are secured together by first coupling the xe2x80x9cbase pipesxe2x80x9d of adjacent joints together and then individually, fluidly connecting each of the shunt conduits on a joint to its respective shunt conduit on the adjacent joint. A typical joint normally has a plurality of parallel, axially-extending shunt tubes thereon. Individual connectors are required for making the necessary fluid connections between the shunt conduits of adjacent joints. Typically, the connector is assembled onto the aligned shunt tubes after the joints have been connected together. The respective shunt tubes on adjacent joints must be substantially in axial alignment before a connection can be made. This tedious assembly adds substantially to the time and overall costs involved in using these alternate path well screens.
One proposed technique is contained in U.S. Pat. No. 5,390,966, which is incorporated herein by reference. A connector is provided for connecting the respective, aligned shunt conduits carried by two adjacent joints of a well tool. The shunt tubes are individually, fluidly connected. The connector is slidably positioned on the base pipe at one end of a screen joint. After the base pipes on adjacent joints have been coupled together, the shunt conduits on the joints are aligned and the connector is moved to its xe2x80x9cconnected positionxe2x80x9d in a separate operation. The connector is slid downward on the base pipe and over the coupling between the joints. This device still requires that each shunt tube be substantially aligned with its respective shunt tube on an adjacent joint before the connector will function.
U.S. Pat. No. 5,868,200, which is incorporated herein by reference, discusses an alternate-path, well screen made-up of joints and having a sleeve positioned between the ends of adjacent joints which acts as a manifold for fluidly-connecting the alternate-paths on one joint with the alternate-paths on an adjacent joint. The alternate flowpaths (e.g., shunt tubes) have a plurality of openings spaced along their length, extend longitudinally along the length of the joint and are open at both ends. The alternate flowpaths are positioned about the external surface of the screen. The sleeve extends between the adjacent joints, so that it surrounds the lower ends of the upper shunt tubes and the upper ends of the lower shunt tubes. The sleeve is connected at one end to the lower end of the upper screen joint and at its other end to the upper end of the lower screen joint.
Another problem that may arise in typical alternate-path well screens is in maintaining adequate and consistent flow of fluid through the relatively small perforations (or xe2x80x9cexit portsxe2x80x9d) at each of the delivery points along the lengths of the bypass tubes. For example, the flow of the gravel-laden slurry in a gravel pack operation is substantially parallel to the axis of the delivery or shunt tubes until the slurry reaches the respective exit ports along the length of a shunt tube. The flow must then make a xe2x80x9cright-anglexe2x80x9d turn before it can flow through a respective exit port. This results in a tendency for at least some of the particulates (i.e., sand) to by-pass the ports. This, in turn, causes the sand concentration of the carrier fluid to build-up inside the shunt tube thereby adversely affecting the distribution of the gravel pack. In fracturing operations, at least a portion of any particles (e.g., sand) in the fracturing fluid will have the same tendency to by-pass the exit ports and build-up within the delivery conduit of the tool. This results in a diluted fracturing fluid (i.e., lower concentration of sand) being delivered through the exit ports. Further, in order to maintain the proper pressures at each level along the tool and to prevent premature dehydration of the slurry, each of the exit ports must be relatively small. Unfortunately, the small size (e.g., diameter) of the exit ports severely restricts the volume of fracturing fluid, which can be delivered to each fracturing level thereby further adversely affecting the fracturing operation. Too many holes will provide too much leak-off from the shunts and reduce shunt fluid velocities. Plugging of smaller shunt holes is also a problem.
Of course, non-uniform concentration of sand being delivered through the individual alternate-paths is also a problem when the slurry flowing in some of the bypass conduits attains a high sand concentration, e.g., due to excessive fluid loss to the unconsolidated formation, while in other conduits the slurry has a higher fluid content.
Thus, there are needs for improved methods and apparatus for completing wells, including providing a simpler, more cost-effective system that uses the alternate path or xe2x80x9cbridging bypassxe2x80x9d phenomenon to enhance gravel packing and fracturing operations.
The present invention provides improved methods and apparatus for completing wells, including gravel packing, fracturing and frac packing operations, which meet the needs described above and overcome the deficiencies of the prior art. The present invention provides an alternate-path, well screen without requiring that the alternate paths (e.g., bypass tubes or conduits) on adjacent joints of screen be axially aligned or individually connected. This allows the joints to be made-up quickly which speeds up the assembly and installation of the alternate-path, well screen.
Improved methods are provided including the steps of placing in the wellbore a perforated shroud (liner) having an internal sand screen therein (e.g., screens, screened pipes, slotted liners, prepacked screens, etc.), positioning about the perforated liner an alternate flowpath comprised of a plurality of xe2x80x9cbypassxe2x80x9d tubes or conduits having inlet passages or portions adapted to receive the gravel slurry as it reaches the apparatus and outlets for the slurry to reach the well annulus, and injecting particulate material (e.g., slurry) into the wellbore wall/perforated liner annulus and perforated liner/screen annulus, whereby the particulate portion of the slurry is uniformly packed into the two annuli. The permeable pack of particulate material formed prevents the migration of formation fines and sand with fluids produced into the wellbore from an unconsolidated zone.
The bypass tubes may be positioned inside the perforated shroud or liner (externally of the sand screen) or outside the perforated shroud. If the tubes are located inside the perforated shroud (liner), no structure projecting outside the perforated shroud (liner) is provided and therefore, the danger of the perforated shroud sticking to the wellbore when the perforated shroud is lowered or lifted through the wellbore is minimized.
In one aspect of the invention, alternate flowpaths comprising relatively short, blank tubes are attached inside the perforated liner (externally of the sand screen). The tubes extend in the axial direction of the perforated shroud and are spaced at predetermined intervals in the circumferential direction of the shroud. For purposes of this embodiment, the term xe2x80x9cblank tubexe2x80x9d denotes a structure forming an elongated, closed fluid passageway effectively having only two spaced opening points for flow into and out of the passageway.
The tubes have inlet passages or portions adapted to receive the gravel slurry as it reaches the apparatus and outlets to direct the slurry to the interval. The upper and/or lower ends of the tubes may (but are not required to) be open and/or have a tapered, arcuate or beveled shape. In one example, the open, lower ends of the bypass tubes comprise the outlets for the slurry to reach the well annulus. Each of the tubes extends only a portion of the length of the shroud, so the tube outlets (e.g., open lower ends of the respective tubes) are spaced at intervals along the length of the shroud. The bypass tubes or conduits provide alternate flow paths for the sand-laden fluid to reach the well annulus via outlets which are relatively larger in area (than the shunt-tube perforations used to deliver the slurry in typical alternate-path well screens), so larger volumes of fluid can be delivered and premature dehydration of the slurry and/or sand build-up within the tubes is inhibited.
The use of the relatively larger (in area) open, lower ends of the bypass tubes to deliver the slurry to the well annulus alleviates the problem of the exit ports along the length of a typical shunt tube often becoming blocked with sand prior to the completion of the operation. For example, if a sand bridge forms in the annulus between the perforated liner and the wellbore, the slurry is still free to flow through the tubes and out into the annulus through the outlets of the tubes to complete the filling of the annulus above and/or below the sand bridge.
The present alternate-path, well screen can be comprised of one or more basically identical pipe joints (xe2x80x9cscreen unitsxe2x80x9d or xe2x80x9cscreen jointsxe2x80x9d). A threaded coupling or the like may be provided on either end of the pipe joints to connect adjacent joints together. The improved well screen may have a crossover sub or the like attached at its upper end which, in turn, is connected to and suspended in the wellbore by a work string or tubing string.
The bypass tubes are mounted or attached to the perforated liner or shroud. In one aspect of the invention, the tubes are not directly attached to the sand control screen, and the sand screen can be simply slid down inside the perforated shroud during its placement at the wellsite. The perforated shroud has a plurality of openings in the wall thereof to allow fluid from the outlets of the bypass tubes to flow through the shroud and into the well annulus during a gravel pack operation and for fluids to flow into the shroud and through the sand screen during production.
The sand control screen located inside the perforated shroud can be an expandable-screen type screen. The expandable screen can be expanded all the way out to the inside wall (ID) of the perforated shroud, allowing the screen to obtain maximum size if desired. The inner annulus between the shroud and the expanded screen no longer exists, but the alternate flow paths are provided via the attached tubes on the shroud. The number of holes or the hole size on the shroud can be increased to minimize flow restriction into the screen during well production.
In another aspect of the present invention, a plurality of axially-spaced xe2x80x9cbundlesxe2x80x9d or series of circumferentially-spaced, axially-extending conduits (e.g., bypass tubes) are provided along the perforated shroud. In one embodiment, the individual bypass tubes comprising each series of conduits are generally parallel to one another and substantially the same length. A connector (or xe2x80x9cmixerxe2x80x9d) is positioned between adjacent tube series which fluidly connect the tubes (as a group) in one series with the tubes in an adjacent series. The connectors may be spaced at intervals along the shroud instead of being located only at the joints between adjacent screen units. The connectors can be separately formed, or they can be formed together with the perforated shroud (liner). At the location of the connectors, the shroud has no perforations but becomes a liner to provide isolation for mixing, and there is no opening between the perforated shroud and the connector. The connectors allow the slurry being transported down the individual bypass tubes to be mixed at intervals prior to entering the tubes below. The bypass tubes need not be individually axially-aligned or fluidly connected with one another. The tubes have inlets for receiving slurry flow. The connectors may have outlet portions for the slurry to reach the well annulus. Where the perforated shroud is of a substantial length, or the distance between connectors is substantial, the bypass tubes preferably have at least one outlet along their length for the slurry to reach the wellbore.
The present methods can be combined with other techniques, such as prepacking, fracturing, chemical consolidation, etc. The methods may be applied at the time of completion or later in the well""s life. The unconsolidated formation can be fractured prior to or during the injection of the particulate material into the unconsolidated producing zone, and the particulate material can be deposited in the fractures, as well as in the wellbore/shroud and shroud/screen annuli.
The improved methods and apparatus of this invention provide a simpler, more cost-effective system with multiple paths, so that a slurry can bypass any premature annulus bridges that form during gravel packing or frac packing and halt the packing process. The system may be used in long intervals and variable formations.
Other and further objects, features and advantages of the present invention will be readily apparent to those skilled in the art upon a reading of the description of preferred embodiments which follows when taken in conjunction with the accompanying drawings, in which: